Electrical contact brush



2 Sheets-Sheet INVHV & K

TOR. GEORGE D. RITTER ATTORNEY Nov. 12, 1957 s. D. RITTER ELECTRICALCONTACT BRUSH M v I 3 m, 94% 5 7 Filed April 20. 1954 Nov. 12, 1957 G.D. RITTER 2,313,203

- ELECTRICAL CONTACT BRUSH Filed April 20. 1954 2 Sheets-Sheet 2 FIG. 8

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ATTORREY United States Patent ELECTRICAL CONTACT BRUSH George D. Ritter,Uniontown, Ohio Application April 20, 1954, Serial No. 424,433

8 Claims. (Cl. 310-247) This invention relates to an electrical contactbrush of the type used to provide sliding electrical contact inelectrical machines.

The invention has particular application in small commutator-typeelectric motors having a pair of springpressed contact brushes, usuallyof carbon or graphite, which apply a voltage to the armature by makingsliding contact with a rotating commutator. These brushes are subjectedto substantial frictional Wear, and also to a certain degree electricalarcing, such that the commutatorcontacting ends of the brushes areslowly consumed or reduced until they become too short to operateproperly and consequently must be replaced. If replacement is not madepromptly, when a brush does become too short to operate properly, theusual metal spring which urges the brush against the commutator eitherfeeds against a part of the brush holder and leaves the brush withouttension or else continues to follow the brush until it touches thecommutator; In either event, the commutator is subjected to seriousdamage from excessive wear and arcing.

It is the chief object of this invention to prevent the occurrence ofsuch damage by providing an improved brush unit for a motor, forexample, which will automatically urge the spring-pressed contact brushaway from contact with the motor commutator, when a prede-.

termined portion of the contact end of the brush has been consumed bynatural wear, thus breaking the usual armature circuit and stopping themotor.

Further objects of the invention are to provide various embodimentswhich are simple in construction, inexpensive to manufacture anddependable in operation. All embodiments, however, make use of aspring-loaded plunger located in the upper portion of the contact brushand so arranged as to be the sole contact with the commutator upon beingreleased by the wearing away of the brush material normally restrainingsaid plunger. When released electrically the end of the plunger whichpushes against the commutator is insulated from the contacting portionof the brush assembly, whereby upon contact of the plunger with thecommutator the motor is stopped.

These and other objects of the invention will be manifest from thefollowing brief description and the accompanying drawings.

Of the accompanying drawings:

Figure 1 is a fragmentary cross-sectional view of an electric motor,having therein a contact brush unit embodying the features of theinvention in inoperative condition.

Figure 2 is a vertically transverse cross-section, on a larger scale,taken substantially on the line 2-2 of Figure 1.

Figure 3 is a cross-section which is the same as Figure 2, except thatit illustrates a worn condition of the contact brush in which the motoris rendered inoperative.

Figures 4 and 5 are vertical cross-sections illustrating modified formsof brush bodies.

Figure 6 illustrates a vertical cross-section of a modified form ofsafety plunger utilized with the brush unit of Figures 1 to 3.

Figures 7 and 8 are cross-sections corresponding to Figures 2 and 3,respectively, but illustrating a modified form of brush unit.

Referring particularly to Figures 1 and 2 of the drawings, a brushholder unit 10 is shown mounted in a housing 11 of an electric motor 12,in association with the usual motor commutator 13, and in conjunctionwith an oppositely disposed like brush holder unit (not shown). Brushholder unit 10 may include a contact brush or member 14, embodying thefeatures of the invention, axially slidably received in anelectro-conductive metal sleeve 15 which is in turn secured within aninsulating sleeve 16 secured in an opening 16a through the wall of motorcasing 11, the inner or contact end of brush 14 normally beingyieldingly pressed against the commutator 13 by a compression spring 17connected between the outer end of the contact brush and a cap 18removably threaded in the outer end of metal sleeve 15. The cap 18 isremovable for ready installation or replacement of the contact brush 14and associated parts. The improved contact brush 14 may be of the usualround or rectangular cross-section, and made of suitableelectro-conductive material, such as carbon or graphite.

Safety means is provided to prevent damage to the motor upon the brush14 becoming substantially worn, as described above. Accordingly,extending axially to be a substantial depth from the outer end of thebrush may be a cylindrical bore 19 (see Figure 2) within which ispress-fitted or otherwise attached a hollow metal retainer sleeve 20,which protrudes beyond the outer end of the brush. Also, a plungerelement 22 is axially shiftably mounted within retainer sleeve 20 to beyieldingly pressed against the normally solid inner end of said bore 19,said element being of electrical insulating material, such as bakelite,ceramic, hard rubber or fiber. For urging said plunger into saidyielding contact with the inner end of bore 19, the plunger 22 is shownprovided with a reduced stem portion 23 defining an annular shoulder 24,between which shoulder and a backing wall 25, provided at the outer endof the retainer sleeve 20, may extend a compression spring 26. In orderto accomplish most efiiicient operation of the plunger in use, as willbe described later, the inner end of bore 19 may terminate in an annulargroove 27 defining an axially outwardly convex protuberance which isnormally yieldingly engaged by an oppositely convex inner face portion28 of the plunger.

In addition to provision of a press-fit between sleeve 20 and brush 14,the contacting surfaces of these two parts may also be bonded withsuitable cement to insure against loosening of the parts during the lifeof the brush assembly.

A section of shunt wire 29 may be soldered or otherwise connectedbetween the top of metal retainer sleeve 2%) and a metal disc 30 backedagainst removable cap 18, thereby providing an electrical conductor tothe brush through said retainer. Thus, the complete brush assembly mayinclude the encased plunger 22 and spring 26, shunt wire 29, cap or disc30, and spring 17. For this purpose the outer end of spring 17 is shownengaging disc 30 to hold it backed against threaded cap 18.

The arrangement of parts described above completes a conductive pathbetween leads 32 of two such brush units 10 through which an electriccurrent can pass. Included in this path are two brushes 14 and theirrespective brush holders 15, shunts 29, caps 30, etc., the bars ofcommutator l3 normally constantly contacted by said brushes, and theusual winding in armature 33 of the motor. As longas both brushes ldof.the motor are in electrical contact with cornmutatorlS the motor maybeoperated; On the otherhand, the armatur will not rotate, as a motor,unless current passing. through its winding and as a flow of currentdepends on both brushes making contact with the commutator 13,it'follows that if either brush were pushed away from the commutator asufficient distance to breal contact the motor would stop operating,This s ould be kept in mind in connection with subsequent explanation-ofthe operationof the improved brush assembly embodying theabove-described specific features of the invention.

In use of the invention in connection with an electric motor 12 asdescribed, the safety feature of the improved brush assembly does notcome into play until at least one brush has become worn to a point wherethe commutator-bearing surface thereof extends across the innermost endof the respective brush bore 19, Whereby, as shown in Figure 3, thedielectric plunger 22 will be urged outwardly of the bore and intocontact with the commutator 13, the spring 26 at the same time beingsufiiciently strong to overcome whatever predeterminate compressivestrength remains in compression spring 17 and urge the brush out ofeffective electrical contact with commutator 13, and otherwisepreventing damage to themotor by cutting off current to the armature 33.The motor can be operated again only after replacement of the worn brushassembly.

Figures 4 and show modified forms of brush members corresponding tobrush member 14, as best shown in Figure 2, but having different shapesof inner end walls 34 which simplify manufacture by certain methods.

Figure 6 shows a modified form of plunger corresponding to plunger 23 inFigure 2, but being a metal pin 35 having an enlarged head or plungerpart 36 covered with a layer of dielectric material.

Figure 7 corresponding to Figure 2, shows a brush holder unit 37, whichincludes in operative condition a modified form of brush assembly 38,incorporated in substantially the same brush-mounting or brush-holdingmeans as before, like numerals being given to the same parts, unlessotherwise noted.

A brush member 39, of the same suitable shape and material as brush 14,however, may have a cylindrical recess or bore 40 extending axiallyinwardly from the outer end thereof to somewhat less than half theoriginal length of the brush, and a cylindrical pin or plunger 42 ofhard insulating material axially slidably received in said bore isspring-pressed toward stop engagement of the inner end of the pin withthe corresponding end of the bore. For this purpose, the outer end ofthe pin 42 has a slot 43 therein retaining a cross-piece d4 of adouble-acting spring 45, to have a compression spring part 46compressively extended between the and a disc 47 backedagainst screw cap13 threaded in the outer end of brush holder sleeve i5. Thus, the springpart 46 by pressing the pin inwardly against the inner endof the bore49, also serves to urge brush member 39 into electrical contact withcommutator An integral'tension spring part 48 of spring extends inwardlyof cross-piece 44 and has its inner end firmly anchored to a reducedneck portion oi 1e outer end of brush 39, the arrangement being such 48is maintained under tension, but is r tiveto urge the pin relative tothe brush. 7

In use of the brush unit of Figure 7 the brush 39 will, by continuedspring-pressed contact with rotating cornmutator as before, eventuallybecome shortened by wear to a point at which 'bore 4% will be opened atits inner end, as shown in Figure 8. At this point spring part 46 willurge the pin 42 to break through'the inner end of the brush into directcontact. withcommutator "13, and at the same time the normally extendedtension spring part 48 will be allowed to contract and thereby draw thebrush out of electrical contact with the commutator (see Figure 8). Inthis way, as in the case of the brush unit shown in Figures 1 to 3,predetermined maximum wear on thebrush-prevents damage to the motor bycutting ofi current to the armature 33.

Other modifications of the invention. may be resorted to withoutdeparting from the spirit thereof or the scope of the appended claims.

What is claimed is: V

l. A contact brush adapted to fit in the usual brush holder unit ofan'electrical machine for providing electrical contact with a movablepart of said machine, comprising a contact member axially shiftable insaid unit, said contact member having an inner contact end and anopposite end, spring means connected to said opposite end pf said memberadaptedin use to yieldingly urge the member into contact of said contactend thereof with said moving part, said member having a recess in saidopposite end extending. to substantial depth axially of the member, adielectric element received in said member recess, and resilient meansbetween the member and element yieldingly tending to urge said elementinwardly of the member, whereby upon said member being worn in use topoint of opening said inner end of said member recess said. element isurged by said resilient means toward sole contact with said movablepart, said element having a portion protruding axially outwardly fromsaid recess of the member, said spring means including a compressionspring compressively extended axially outward from said protrudingportion of said element and a tension spring tensionally connectedbetween the protruding portion of the element andthe member. 7

2. A contact'brush adapted to fit in the usual brush holder unit of anelectrical machine for providing electrical contact with a'movable partof said machine, comprising a contact member axially shiftable in saidunit, said contact member having aninner contact end and an oppositeend, spring means connected to said opposite end of said member adaptedin use to yieldingly urge the member into contact of said contact endthereof with said moving part, said member having a recess in saidoppoiste end extending to substantial depth axially ward from saidprotruding portion of said element and a a tension spring tensionallyconnected bet veen the protruding portion of the element and the member,said tension spring being an integral extension of said compressionspring and connected thereto by a cross-piece, said' protruding portionof said element having a recess in the end'thereof receiving saidcross-piece.

3. A contact brush adapted to fit in the usual brush holder unit of anelectrical machine for providing electrical contact with a movable partof said machine, comprising a contact member axially shiftable in saidunit, said contact member having an inner contact end and an oppositeend, a cylindrical recess in said opposite end extending to substantialdepth axially of the member, a dielectric element received in saidrecess with a sliding fit, said element having a length greater than thedepth of the recess and thus leaving a protruding end, a com pressionspring connected to the protruding end of said element and extendingoutwardly therefrom adapted in use to 'yielding'ly maintain contactbetween said contact end of the member and said movable part, and atension spring tensionally connected between the protruding end of saidelement and said opposite end of the member, whereby upon said memberbeing worn down in use to point of opening the inner end of said recesssaid member is retracted leaving said dielectric element in sole contactwith said movable part, said tension spring being an integral extensionof said compression spring and connected thereto by a cross-piece, saidprotruding end of said element having a recess receiving saidcrosspiece.

4. A contact brush adapted to fit in the usual brush holder unit of anelectrical machine for providing electrical contact with a movable partof said machine, comprising a contact member axially shiftable in saidunit, said contact member having an inner contact end and an oppositeend, said member having a recess in said opposite end extending tosubstantial depth axially of the member, a dielectric element sfidablyreceived in said recess, compression spring means extending between theend of said element outwardly of said recess and a fixed part of theholder unit adapted in use yieldingly to maintain contact between saidcontact end of the member and said movable part, and a tension springtensionally connected between the said element and said opposite end ofthe member and operable upon said member being worn down in use to pointof opening the inner end of said recess to retract said member, andthereby leaving said dielectric element in sole contact with saidmovable part, said tension spring being an integral extension of saidcompression spring and having a cross-piece connected to the end of saidelement outwardly of said member recess.

5. A contact brush adapted to fit in the usual brush holder unit of anelectrical machine for providing electrical contact with a movable partof said machine, comprising a contact member axially shiftable in saidunit, said contact member having an inner contact and and an oppositeend, said member having a recess in said opposite end extending tosubstantial depth axially of the member, a dielectric element slidablyreceived in said recess, compression spring means extending between theend of said element outwardly of said recess and a fixed part of theholder unit adapted in use yieldingly to maintain contact between saidcontact end of the member and said movable part, and a tension springtensionally connected between the said element and said opposite end ofthe member and operable upon said member being worn down in use to pointof opening the inner end of said recess to retract said member, andthereby leaving said dielectric element in sole contact with saidmovable part.

6. In a contact brush adapted to fit in the usual brush holder of anelectrical machine for providing electrical contact with a movable partof said machine, a contact member adapted to be axially shiftable in asaid brush holder, said contact member having-a contact end and anopposite end, said member having a cylindrical bore extending axiallyinwardly from said opposite end to within a predetermined distance ofsaid contact end, an insulated pushing element slidably received in saidbore, pressure means adapted in normal use yieldingly to urge saidelement against the inner end of said bore and thereby through saidelement to maintain contact between said contact end of the member andsaid movable part, and spring means connected between said element andsaid member and operable independently of said pressure means upon saidcontact end being worn away a said predetermined distance to urge saidcontact member away from said movable part, and thereby leaving said insulated pushing element in sole contact with the said movable part.

7. In a contact brush adapted to fit in the usual brush holder of anelectrical machine for providing electrical contact with a movable partof said machine, a contact member adapted to be axially shiftable in asaid brush holder, said contact member having a contact end and anopposite end, said member having a cylindrical bore extending axiallyinwardly from said opposite end to within a predetermined distance ofsaid contact end, an insulated pushing element slidably received in saidbore, pressure means adapted in normal use yieldingly to urge saidelement against the inner end of said bore and thereby through saidelement to maintain contact between said contact end of the member andsaid movable part, and spring means connected between said element andsaid member and operable independently of said pressure means upon saidcontact end being worn away a said predetermined distance to urge saidcontact member away from said movable part, and thereby leaving saidinsulated pushing element in sole contact with the said movable part,the inner end of said bore terminating in a peripheral groove defining acentral protuberance adapted to separate from said member substantiallyas soon as the wear on said member reaches the innermost depth of saidgroove. 7

8, In a contact brush adapted to fit the usual brush holder of anelectrical machine for providing electrical contact with a movable partof said machine, a contact member of electro-conductive material adaptedto be axially shiftable when in use with said brush holder, said contactmember having a contact end and an opposite end, said member having arecess extending in a substantially axial direction inwardly from saidopposite end to within a predetermined distance of said contact end, aninsulated pushing element received in said recess, pressure meansadapted in normal use yieldingly to urge said element against the innerend of said recess and thereby through said element to maintain contactbetween said contact end of the member and said movable part, and springmeans connected between said element and said member and operableindependently of said pressure means upon said contact end being wornaway a said predetermined distance to urge said contact member away fromsaid movable part, and thereby leaving said insulated pushing element insole contact with the said movable part.

References Cited in the file of this patent FOREIGN PATENTS 577,400Great Britain May 16, 1946 614,404 Germany June 7, 1935 847,307 GermanyAug. 21, 1952

